The efficient and inexpensive production of hydrogen by water electrolysis is a subject attracting worldwide interest. Most exsisting apparatus for water electrolysis are inefficient and expensive. Efforts have been made to raise the efficiency of the water electrolysis so as to produce hydrogen on an industrialscale. For example, U.S. Pat. No. 4,795,537 to Richard R. Timewell discloses an electrical conditioning system for electrodes in an electrolysis cell, in which a pulsating DC voltage is generated and applied to the electrode means to be conditioned in a manner that hydrogen is produced at the cathodic portion of the electrode means and the anodic portion of said electrode means is maintained substantially in a state of passivation. Chinese Patent Application No. 89101949 shows a small sized apparatus for electrolyzing water, which raises the efficiency of water electrolysis by means of a high frequency pulsating DC power source. However, the spacing between the electrodes is relatively large (about 8 mm) and this prevents the efficiency from being further raised.